The paper presents the evaluation of soil water erosion risk of the Mściwojów water reservoir drainage basin. In the present study, modelling with the use of GIS (Geographical Information Systems) and RUSLE (Revised Universal Soil Loss Equation) erosion models were exploited. Values of topographic factor (LS) were calculated after formulas proposed by Moore et al. [1991] as well as Desmet and Govers [1996]. The results of erosion prognosis by means of RUSLE method after Moore’s formula are by 40% higher than values evaluated after Desmet and Gover’s formula. Eroded soil mean mass from area unit during the year is estimated at the level of 10.35–14.53 Mg ∙ ha–1 ∙ year–1, depending on computable formula used. Results of this research enabled to divide the drainage basin area into soil water erosion intensity zones based on predicted soil loss values according to Marks et al. [1989]. The study shows that water erosion risk of soil in the Mściwojów water reservoir drainage basin is very high. Almost one third of its area is located in the high and very high class of erosion risk.